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Project 4

Investigating the evolutionary pathways towards replacement or complementation in the evolution of insect endosymbionts

PhD position. Supervisors: Amparo Latorre (UniValencia) and Martin Embley (UniNewcastle) (with input from Rosario Gil, UniValencia). Host: UniValencia. Secondment internship:to UniNewcastle.

Rationale

Bacterial endosymbionts of insects may evolve in such a way that the primary endosymbiont can be replaced by a secondary one or, alternatively, both of them can form a consortium by metabolic complementation. In our group, we have sequenced the genomes of primary endosymbionts in a very advanced stage of genome reduction. Other extremely reduced genomes of bacterial endosymbionts are also available. Recently, we also finished the genomic sequencing of dual endosymbiotic systems from two aphid species of the family Lachninae, Cinara cedri and C. tujafilina. The first dual system is formed by Buchnera aphidicola Bcc and Serratia symbiotica SCc, constituting an advanced stage of metabolic complementation. By contrast, the second dual system (B. aphidicola Bct and S. symbiotica Sct) is less evolved, and may represent a transtitional phase to either replacement or the establishment of metabolic complementation.

Objectives

There is no clear idea on the causes promoting one or other evolutionary path. The main objective of the project is (i) to simulate the process of genome reduction, in order to evaluate what are the factors determining the evolution towards replacement or complementation. The results obtained (ii) will be empirically tested by comparing genetic, genomic and metabolic information retrieved from the different endosymbiotic systems, as well as population parameters from the corresponding insect hosts. Finally, to evaluate the degree of host-dependence, (iii) we will compare the inferred metabolic networks of endosymbionts of extremely reduced genome sizes with those that represent intermediate stages.

Key methods

This is a computational biology PhD project that requires (i) a well annotated set of bacterial endosymbiont genomes, and updated available bioinformatic packages for (ii) metabolic inference, (iii) phylogenetic and phylogenomic analyses, (iv) statistical testing, and (v) simulation.